In recent years, a demand for attaining a higher electric power density with an electric power conversion device (electric power density =the output electric power of the electric power convertor/the volume of the electric power convertor) is increasing. In order to achieve a higher electric power density, the volume of the electric power conversion device is required to be reduced.
The main portion of the volume of the electric power conversion device is passive components such as a cooling device, a capacitor, and an inductor, and in order to reduce the size of the cooling device, the loss of the electric power convertor needs to be reduced, and in order to reduce the size of a passive component, the switching frequency needs to be increased.
In general, the load of the electric power conversion device includes an inductance component. A basic equivalent circuit of a conventional electric power conversion device is shown in FIG. 1. A basic equivalent circuit of an electric power conversion device of FIG. 1 includes a power supply 1R, a parasitic inductance 2R, a diode 3R (free wheeling diode), a switching element 4R, a load 5R, and a gate circuit 6R.
When the switching element 4R turns on in the equivalent circuit of FIG. 1, an electric current flows through a circuit loop constituted by the power supply 1R, the parasitic inductance 2R, the load 5R, and the switching element 4R.
Subsequently, when the switching element 4R turns off, the electric current flows through the load 5R does not become zero in a very short time since the load 5R includes an inductance component. Therefore, an electric current flows through a circuit loop constituted by the load 5R and the diode 3R. Thereafter, when the switching element 4R turns on again, the circuit loop constituted by the power supply 1R, the parasitic inductance 2R, the load 5R, and the switching element 4R is formed, so that the electric current flowing through the diode 3R decreases, and the electric current flowing through the switching element 4R increases. The turn-on electric current waveform of the switching element 4R at this occasion is shown in FIG. 2.
As described above, when the switching element 4R turns on in the conventional electric power conversion device, a high frequency oscillation occurs in an electric current waveform, which becomes a noise source.